The U.S. budget gap widened in the first half of the fiscal year as spending rose faster than revenue.

The government ran a $691 billion deficit from October through March, the Treasury Department said on Wednesday, compared with $600 billion during the same period a year earlier.

The Treasury Department said spending has driven the 2019 fiscal deficit increase. Federal outlays rose 5%, to $2.198 trillion in the October-through-March period, while revenues increased 1%, to $1.507 trillion.

More broadly, deficits are projected to climb in the coming decades as an aging U.S. population fuels higher costs for programs such as Social Security and Medicare. The Congressional Budget Office projects deficits as a share of gross domestic product will average 4.4% over the next 10 years, compared with a 2.9% average over the previous 50 years.

The fiscal outlook will be the focus of policy negotiations in Congress this year as lawmakers work toward a new two-year agreement to set top-line government spending levels, and to avoid automatic spending cuts set to kick in after October.

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